Presently known magnetic disk drives typically include magnetic storage disks and head suspension assemblies having air bearing sliders on which magnetic transducers are disposed. The air bearing sliders in a rigid disk drive fly above the disk surface. In such disk drives, it has been customary to start and stop the operation by a contact start/stop (CSS) process. One design objective of conventional magnetic disk drives is to cause most of the wear to occur at the slider/disk interface during the start and stop stages. Minimal wear during the start and stop stages is crucial but is often difficult to achieve.
A prerequisite to the CSS process is that the surface of the magnetic disk be roughened to a degree sufficient to prevent high stiction that causes the air bearing slider and the disk to adhere while the disk is not in operation. Moreover, in order to meet the demand for increased areal density, efforts have been made to minimize the head flying height, which requires smoother disks.
In light of these design objectives attempts have been made to decrease the slider size and to design new loading/unloading mechanisms for avoiding contact start/stop.
Conventionally, a constant gram load is provided to the head suspension for loading the magnetic head to the disk. The gram load acts to counterbalance the effect of the air bearing lift force. However, when the air bearing lift force is removed, the head contacts the disk, thus generating wear and debris, and compromising data integrity, which could eventually lead to a head crash.
Dynamic head loading/unloading mechanisms have been designed to maintain an acceptable flying height of the head over the disk. U.S. Pat. Nos. 5,289,325; 5,237,472; 5,469,314; and 5,486,964 to Morehouse et al. are exemplary of a rigid disk drive with a dynamic head loading/unloading apparatus. The disk drive includes a rotary actuator having a lift tab that extends asymmetrically from the end of the load beam. The free end of the lift tab cooperates with a cam surface on a cam assembly to provide dynamic loading and unloading of the slider while imparting a roll to the slider as it is loaded to and unloaded from the disk.
While these dynamic loading/unloading mechanisms may have solved certain concerns associated with prior static loading/unloading mechanisms, they still suffer from several drawbacks. The dynamic loading/unloading mechanisms have relatively complex designs, and they require a very tightly controlled loading angle. In addition, the loading/unloading cam prevents the optimization of the z-height of the suspension, that is the distance between the suspension mounting surface and the disk surface.
Furthermore, under a constant preload, the flying height of some slider air bearing designs, e.g., twin rail taper flat, is not uniform, but is typically lower at the inner diameter (ID) of the disk than at the outer diameter (OD). The radial dynamic loading on a ramp forces the slider to develop an air bearing with a severe initial roll increasing the likelihood of a head crash. In addition, the ramp loading scheme lacks the precision control intrinsic in a finely controlled rotational speed and acceleration of the disk.
Conventional disk drives are altitude sensitive. As the altitude increases, the flying height decreases so that the air bearing force could counteract the constant preload.